OC 08.1 - High rate of recurrent thrombosis in children with unprovoked venous thromboembolism

Background: The high risk of recurrent venous thromboembolism (VTE) in adults with unprovoked VTE led to recommendations for prolonged anticoagulation. Little evidence guides anticoagulation duration for pediatric unprovoked VTE.

Aims: Estimate the incidence of recurrent VTE in children with unprovoked VTE and evaluate characteristics associated with recurrence.

Methods: We performed a single center, retrospective study including children aged 1- < 21 years with unprovoked index VTE between 1/1/2003 – 8/1/2021. Patients were followed from first VTE until recurrent VTE or censoring (death, age 21 years, or date of last contact). Analysis included descriptive statistics and estimated incidence of recurrent VTE with 95% confidence interval (CI). Time to recurrent VTE was modeled with Kaplan-Meier estimator, and we compared the hazard of recurrence according to thrombophilia, age, and sex with univariate Cox proportional hazards regression. The Institutional Review Board exempted this study and the National Institutes of Health support HW.

Results: 85 children met inclusion criteria (Table 1) with 26 recurrent events in 250.26 person-years (incidence rate = 104 [95% CI: 71 – 153] per 1000 person-years). 61% (95% CI: 46 – 73%) of children were free from recurrent VTE at 5 years (Figure 1). Univariate analysis demonstrated a higher hazard of recurrence associated with age at first VTE ≥12 years (HR 7.56, 95% CI: 1.60-35.83). There was no association with sex (HR 0.56, 95% CI: 0.25-1.27). When compared to no thrombophilia, low-risk thrombophilia was not associated with recurrence (HR 0.89, 95% CI: 0.20-3.96), however high-risk thrombophilia was significant (HR 3.27, 95% CI: 1.43-7.46).

Outpatient anticoagulation is summarized in Table 1. One patient recurred during the index VTE admission and was excluded from anticoagulation analysis. 12 of 26 (46%) had recurrent VTE on anticoagulation.

Conclusion(s): We demonstrate a high rate of recurrent VTE in children with unprovoked VTE, especially those ≥ 12 years or with a high-risk thrombophilia.